Method and device for determining wheel slip information of an electrically driven wheel of a motor vehicle

Abstract

A method and a device for determining wheel slip information of an electrically driven wheel of a motor vehicle, according to which during travel, the speed (nE-motor) of an electric motor driving the wheel is detected and the detected speed (nE-motor) of the electric motor is used to determine the wheel slip information.

The invention claimed is: 
     
       1. A method for determining wheel slip information of an electrically driven wheel comprising:
 a motor vehicle, according to which during travel, when a wheel speed sensor for the electrically driven wheel fails, a speed (n E-motor ) of an electric motor driving the wheel is calculated from a current profile and/or a voltage drop and/or from information about control of the motor, and the calculated speed (n E-motor ) of the electric motor is used to determine the wheel slip information, wherein the wheels of an axle are driven via a common electric motor and an axle differential, and a speed difference (Δn) between the wheels of the axle caused by the axle differential is detected, 
 wherein a theoretical wheel speed (n wheel,theo ) is determined from the calculated speed (n E-motor ) of the electric motor, the speed difference (Δn), and a gear ratio and axle differential ratio (i G , i A ) for both wheels of the axle, and in that an actual wheel speed (n wheel,actual ) of the wheels of the axle is determined from a current driving speed (V vehicle ) of the motor vehicle, wherein when the theoretical wheel speed (n wheel,theo ) of one or more wheels deviates from the actual wheel speed (n wheel,actual ), it is determined as wheel slip information that the wheel in question or both wheels of the axle is/are slipping. 
 
     
     
       2. The method according to  claim 1 , wherein each electrically driven wheel is assigned a separate electric motor. 
     
     
       3. The method according to  claim 2 , wherein the theoretical wheel speed (n wheel,theo ) of the wheel is calculated according to the formula 
       
         
           
             
               
                 n 
                 
                   wheel 
                   , 
                   theo 
                 
               
               = 
               
                 
                   n 
                   
                     E 
                     ⁢ 
                     
                       - 
                     
                     ⁢ 
                     Motor 
                   
                 
                 
                   i 
                   G 
                 
               
             
           
         
       
       and
 the actual wheel speed (n wheel,actual ) of the wheel is calculated according to the formula 
 
       
         
           
             
               
                 n 
                 
                   wheel 
                   , 
                   left 
                   , 
                   actual 
                 
               
               = 
               
                 
                   V 
                   vehicle 
                 
                 
                   π 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     d 
                     wheel 
                   
                 
               
             
           
         
       
       wherein d wheel =diameter of the wheel. 
     
     
       4. The method according to  claim 1 , wherein the theoretical wheel speed (n wheel,theo ) of the wheels of the axle is calculated according to the formula 
       
         
           
             
               
                 n 
                 
                   wheel 
                   , 
                   theo 
                 
               
               = 
               
                 
                   1 
                   2 
                 
                 ⁢ 
                 
                   ( 
                   
                     
                       
                         n 
                         
                           E 
                           ⁢ 
                           
                             - 
                           
                           ⁢ 
                           motor 
                         
                       
                       
                         
                           i 
                           G 
                         
                         ⁢ 
                         
                           i 
                           A 
                         
                       
                     
                     ± 
                     
                       Δ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       n 
                     
                   
                   ) 
                 
               
             
           
         
       
       and
 the actual wheel speed (n wheel,actual ) of the wheels of the axle is calculated according to the formula 
 
       
         
           
             
               
                 
                   n 
                   
                     wheel 
                     , 
                     actual 
                   
                 
                 = 
                 
                   
                     V 
                     vehicle 
                   
                   
                     π 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       d 
                       wheel 
                     
                   
                 
               
               , 
               
                 
                   wherein 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     d 
                     wheel 
                   
                 
                 = 
                 
                   diameter 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   of 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   the 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     wheel 
                     . 
                   
                 
               
             
           
         
       
     
     
       5. The method according to  claim 1 , wherein the actual wheel speed (n wheel,actual ) deviates from the theoretical wheel speed when the following applies to the wheel speeds:
   n wheel,actual ≤0.9 n wheel,theo  or n wheel,actual ≥1.1n wheel,theo.  
 
 
     
     
       6. The method according to  claim 2 , wherein the actual wheel speed (n wheel,actual ) deviates from the theoretical wheel speed when the following applies to the wheel speeds:
   n wheel,actual ≤0.9 n wheel,theo  or n wheel,actual ≥1.1 n wheel,theo.  
 
 
     
     
       7. A device for determining wheel slip information of an electrically driven wheel of a motor vehicle when a wheel speed sensor for the electrically driven wheel fails, comprising:
 an electric motor for driving the wheel, the wheel speed sensor assigned to the wheel, and a regulating/control unit configured for calculating a speed (n E-motor ) of the electric motor, wherein the current motor vehicle speed (V vehicle ), the output signals of the wheel speed sensor, the speed (n E-motor ) of the electric motor, and at least one of a voltage, current, or control signal for the electric motor, are provided as input signals to the regulating/control unit, 
 wherein the regulating/control unit is configured to determine wheel slip information using the input signals when the wheel speed sensor fails, wherein one or more wheels of an axle are driven via a common electric motor and an axle differential, and a speed difference (Δn) between the wheels of the axle caused by the axle differential is detected, 
 wherein a theoretical wheel speed (n wheel,theo ) is determined from the calculated speed (n E-motor ) of the electric motor, the speed difference (Δn), and a gear ratio and axle differential ratio (i G , i A ) for both wheels of the axle, and in that an actual wheel speed (n wheel,actual ) of the wheels of the axle is determined from a current driving speed (V vehicle ) of the motor vehicle, wherein when the theoretical wheel speed (n wheel,theo ) of one or both wheels deviates from the actual wheel speed (n wheel,actual ), it is determined as wheel slip information that the wheel in question or both wheels of the axle is/are slipping.